diff --git a/src/Analyser/TypeSpecifier.php b/src/Analyser/TypeSpecifier.php
index e5bd2bbd57..b279185906 100644
--- a/src/Analyser/TypeSpecifier.php
+++ b/src/Analyser/TypeSpecifier.php
@@ -196,6 +196,8 @@ public function specifyTypesInCondition(
 				$context,
 				$rootExpr,
 			);
+		} elseif ($expr instanceof Expr\Cast\Bool_) {
+			return $this->resolveEqual(new Expr\BinaryOp\Equal($expr->expr, new ConstFetch(new Name\FullyQualified('true'))), $scope, $context, $rootExpr);
 		} elseif ($expr instanceof Node\Expr\BinaryOp\Equal) {
 			return $this->resolveEqual($expr, $scope, $context, $rootExpr);
 		} elseif ($expr instanceof Node\Expr\BinaryOp\NotEqual) {
diff --git a/tests/PHPStan/Analyser/LegacyNodeScopeResolverTest.php b/tests/PHPStan/Analyser/LegacyNodeScopeResolverTest.php
index 4d0ca33581..1b67568efa 100644
--- a/tests/PHPStan/Analyser/LegacyNodeScopeResolverTest.php
+++ b/tests/PHPStan/Analyser/LegacyNodeScopeResolverTest.php
@@ -355,7 +355,7 @@ public function dataAssignInIf(): array
 				$testScope,
 				'matches3',
 				TrinaryLogic::createYes(),
-				'array{0?: string}',
+				'array{}|array{string}',
 			],
 			[
 				$testScope,
@@ -415,7 +415,7 @@ public function dataAssignInIf(): array
 				$testScope,
 				'ternaryMatches',
 				TrinaryLogic::createYes(),
-				'array{0?: string}',
+				'array{string}',
 			],
 			[
 				$testScope,
diff --git a/tests/PHPStan/Analyser/nsrt/bug-10528.php b/tests/PHPStan/Analyser/nsrt/bug-10528.php
new file mode 100644
index 0000000000..07fe77ade0
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-10528.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace Bug10528;
+
+use function PHPStan\Testing\assertType;
+
+function bug10528(string $string): void {
+	$pos = strpos('*', $string);
+	assert((bool) $pos);
+
+	assertType('int<1, max>', $pos);
+
+	$sub = substr($string, 0, $pos);
+	assert($pos !== FALSE);
+	$sub = substr($string, 0, $pos);
+}
+
diff --git a/tests/PHPStan/Analyser/nsrt/bug-6006.php b/tests/PHPStan/Analyser/nsrt/bug-6006.php
new file mode 100644
index 0000000000..e9ad4e2464
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-6006.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace Bug6006;
+
+use function PHPStan\Testing\assertType;
+
+function bug6006() {
+	/** @var array<string, null|string> $data */
+	$data = [
+		'name' => 'John',
+		'dob' => null,
+	];
+
+	$data = array_filter($data, fn(?string $input): bool => (bool)$input);
+
+	assertType('array<string, non-falsy-string>', $data);
+}
+
+
diff --git a/tests/PHPStan/Analyser/nsrt/bug-7685.php b/tests/PHPStan/Analyser/nsrt/bug-7685.php
new file mode 100644
index 0000000000..580ad7f33f
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-7685.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace bug7685;
+
+use function PHPStan\Testing\assertType;
+
+interface Reader {
+	public function getFilePath(): string|false;
+}
+
+function bug7685(Reader $reader): void {
+	$filePath = $reader->getFilePath();
+	if (false !== (bool) $filePath) {
+		assertType('non-falsy-string', $filePath);
+	}
+}
+
diff --git a/tests/PHPStan/Analyser/nsrt/narrow-bool-cast.php b/tests/PHPStan/Analyser/nsrt/narrow-bool-cast.php
new file mode 100644
index 0000000000..582062deb7
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/narrow-bool-cast.php
@@ -0,0 +1,29 @@
+<?php
+
+namespace NarrowBoolCast;
+
+use function PHPStan\Testing\assertType;
+
+/** @param array<mixed> $arr */
+function doFoo(string $x, array $arr): void {
+	if ((bool) strlen($x)) {
+		assertType('string', $x); // could be non-empty-string
+	} else {
+		assertType('string', $x);
+	}
+	assertType('string', $x);
+
+	if ((bool) array_search($x, $arr, true)) {
+		assertType('non-empty-array', $arr);
+	} else {
+		assertType('array', $arr);
+	}
+	assertType('string', $x);
+
+	if ((bool) preg_match('~.*~', $x, $matches)) {
+		assertType('array{string}', $matches);
+	} else {
+		assertType('array{}', $matches);
+	}
+	assertType('array{}|array{string}', $matches);
+}
diff --git a/tests/PHPStan/Rules/Functions/ReturnTypeRuleTest.php b/tests/PHPStan/Rules/Functions/ReturnTypeRuleTest.php
index 45ddca1767..f16d288869 100644
--- a/tests/PHPStan/Rules/Functions/ReturnTypeRuleTest.php
+++ b/tests/PHPStan/Rules/Functions/ReturnTypeRuleTest.php
@@ -290,4 +290,11 @@ public function testBug11518(): void
 		$this->analyse([__DIR__ . '/data/bug-11518.php'], []);
 	}
 
+	public function testBug8881(): void
+	{
+		$this->checkExplicitMixed = true;
+		$this->checkNullables = true;
+		$this->analyse([__DIR__ . '/data/bug-8881.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Functions/data/bug-8881.php b/tests/PHPStan/Rules/Functions/data/bug-8881.php
new file mode 100644
index 0000000000..85c59c4fae
--- /dev/null
+++ b/tests/PHPStan/Rules/Functions/data/bug-8881.php
@@ -0,0 +1,13 @@
+<?php declare(strict_types=1);
+
+namespace Bug8881;
+
+/**
+ * @param int[] $a
+ * @return int
+ */
+function pop($a)
+{
+	assert((bool)$a);
+	return array_pop($a);
+}